aemfvp-a-rme: script for booting a lkvm guest in realm security state

Adding realm_guest.sh script for launching lkvm guest in realm.
Usecase supports
- booting FVP with stack built bins and images.
- waiting for boot to complete and login to appear.
- launching realm_guest_test script in FVP host to run lkvm guest.
- verifying the lkvm guest has been launched and login appears.

Signed-off-by: nitin sharma <nitin.sharma3@arm.com>
Change-Id: I0f7390e9b304d10f7eeb5c90f34f7fc466cd9892